This invention relates to a system to control the operation of an internal combustion engine, which system is of a type comprising transducers to detect parameters of the engine operating conditions, digital control means for repeatedly executing computing processes by utilizing the detected parameters as input information and at least one actuator whose operation is controlled by the output of the digital control means.
A digital control system of the above stated type is principally constituted of a data treatment device to read in input data necessary for computation processing, a write-and-read type memory device, an arithmetic or arithmetic-logic unit and an output-data conversion device. When a subsystem is operated in places or under conditions where external noises of considerable intensities break out frequently as typified in applications to automobiles, the input and output devices, memory device and the arithmetic-logic unit are liable to be influenced by such external noises and, therefore, there is a danger of the control system producing an erroneous output.
For example, the control system has capabilities to instantly judge that the engine is stalling when the rotational speed of the engine falls below a predetermined value and quickly change its output so as to restore an actuator or actuators each to a preset state. But if an error is made in the estimation of the engine speed it becomes difficult to accurately discriminate between normal operation of the engine and stall of the engine. Sometimes, an erroneous function of a certain part of the control system caused by an external noise results in the control system providing an erroneous output which brings about stalling of the engine. Moreover, there is a possibility that an erroneous function of the control system under the stimulus of noise will cause an actuator to continue an erroneous function which invites danger. For example, danger of fire is incurred when a fuel injection valve is uncontrollably left of in an open state, or an ignition circuit brings on a danger of generating extraordinary heat and/or being damaged by burning when a current is allowed to continue flowing through an ignition coil.
In a broad sense an object of the present invention is to prevent a digital control system for the control of the operation of an internal combustion engine from producing an erroneous output in response to an erroneous input or a noise signal.
It is a primary object of the present invention to provide an improved system for the control of the operation of an internal combustion engine, which system is of the hereinbefore described type and, as the improvement, has the capabilities of accurately recognizing a real stall of the engine without being affected by external noises and then holding its output to at least one actuator in a state prescribed for the case of engine stalling.
The present invention provides a control system which includes sensor means for detecting parameters of operating conditions of an internal combustion engine and a digital control means for repeatedly executing computing processing by utilizing the parameters detected by the sensor means as input information thereby producing a control signal to control the operation of at least one actuator which regulates a factor of operation of the engine. The sensor means include means for producing a pulse signal representative of the rotational speed of the engine. According to the present invention, the digital control means in this control system comprise a comparing means for comparing pulse intervals between two successive pulses of the pulse signal representative of the engine speed with a predetermined length of time and discriminating means for judging that the engine is stalling when the pulse intervals subjected to comparison continue to be longer than the predetermined length of time for another predetermined length of time.
Because of the above stated construction, the control system of the invention does not instantly judge that the engine is stalling when the engine speed signal momentarily implies a considerably low rotational speed but, instead, examines whether the engine speed signal continues to imply such a low engine speed condition for a predetermined period of time. Only when an affirmative result is obtained this control system forms a judgement that the engine is stalling. Since generally noise signals do not exist continuously, this control system can accurately discriminate noise signals from a correct signal which implies a real stall of the engine.
The comparing means may be made to have the function of generating a pulse each time a pulse interval of the engine speed signal becomes longer than a predetermined length of time such that, if the pulse generation is repeated, the pulses are generated at a constant interval. In this case the discriminating means are made to have the capabilities of counting the number of pulses produced by the comparing means and judging that the engine is stalling when the result of the counting reaches a predetermined number.